Recently, the number of patients with cardiovascular diseases associated with aging of the population and changes of eating habits and lifestyle has risen markedly. Since thrombotic diseases such as cerebral infarction, myocardial infarction and peripheral circulatory disorders have not only high morbidity but also result in poor prognosis and limitation on activities of daily living, patients with these disorders have an undue burden of personal and social disability. It is well known that the direct causes of these diseases are angiostenosis caused by thrombus induced by platelet activation (adhesion to damaged areas of blood vessels, release of physiologically active substances, clot formation, and so on) and ischemia associated with angiostenosis. Thus, antithrombotic agents that inhibit platelet activation play important roles in preventing the occurrence and recurrence of these diseases as well as in their treatment. Furthermore, these agents are considered to become more and more important in the future as the number of patients with thrombotic diseases increases.
Several biological substances related to platelet aggregation, such as adenosine 5′-diphosphate (ADP), thromboxane A2 (TXA2), collagen, serotonin (5-HT) and the like, are known. Moreover, P2Y1 and P2Y12 receptors are known as ADP receptors. Some existing antithrombotic agents act by exerting antagonistic action against these receptors. Examples of such antithrombotic agents are ticlopidine and clopidogrel, which have thienopyridine structures.
In addition, compounds as described in WO98/08811 or WO99/43648 are known as compounds having non-thienopyridine structures and antagonistic action against ADP receptors. However, there are certain problems in that these compounds are chemically unstable or only weakly active.